(1) Field of the Invention
The present invention relates to high density fine ceramic sintered bodies useful for engine parts, gas turbine parts, mechanical parts, wear resistant slide members, and the like, and a process for manufacturing the same.
(2) Related Art Statement
In order to produce ceramic products, it is a conventional practice, as shown in a flow chart of FIG. 5 by way of example, to first mix a ceramic raw material with a sintering aid, and then grind the mixture and pass through a sieve of 44 .mu.m to remove foreign matter such as broken pieces of grinding media used for the grinding. Then, after granulating, water is added to the granulated powder as necessary, and the granulated powder is shaped by a mold press or a cold isostatic press. The shaped body is finally sintered at a given temperature to obtain a sintered product.
However, since positive measures are not taken to uniformly disperse water in the granulated powder in the above-mentioned conventional ceramic product-producing process, the amount of water in the granulated powder is locally varied. As a result, pores are formed in the shaped bodies due to nonuniform particle fracture which is caused by nonuniform water distribution in the granulated powder, so that such pores remain in the sintered products. Consequently, ceramic sintered bodies having excellent mechanical characteristics cannot be obtained.
Particularly, when ceramic sintered bodies are used as bearing members, wear resistant members or slide members, pores and hardness largely influences the use life thereof. Thus, in order to obtain ceramic products having longer use life than before, it was necessary to produce high hardness ceramic sintered products having a smaller pore diameter and porosity. Among them, when they are used as bearing materials, it is known that it is important to improve the fatigue life of the materials. Thus, there has been a demand to develop dense, high strength, and/or high hardness ceramic materials to improve rolling fatigue life.